Apollo ALSEP Data Restoration

NSSDCA personnel are completing the restoration of a large number of original
data tapes from the Suprathermal Ion Detector Experiment (SIDE), which was part
of the Apollo Lunar Surface Experiments Package (ALSEP) on the Apollo 12, 14,
and 15 missions. The data are from the two sensors within the SIDE; the Total
Ion Detector (TID) and the Mass Analyzer (MA). The TID measured a 20-channel
differential energy spectrum from 10 eV/Q to 3500 eV/Q. The MA measured a
20-channel mass spectrum at each of six energy levels from 0.2 to 48.6 eV. The
sensors were directional, pointing in the ecliptic plane 15 degrees from the
lunar local meridian. Due to the range of longitudes of the three mission
landing sites, the look directions of the instruments were about 38 degrees
west, 2 degrees west, and 19 degrees east of the Earth for Apollo 12, 14, and
15, respectively. Thus at certain times during the lunar orbit they could see
ion flows in the magnetosheath, but never looked directly at the solar wind.
During other times the detectors saw ion events of several different types;
some appear to be mainly related to the moon and others to the magnetotail.
These instruments resulted in numerous publications and theses. The data have
been used, e.g., to determine the potential of the lunar surface, to determine
the effective plasma screening length at the surface, to study the ion mass
spectra, and to study magnetotail ion fluxes. There was also a rather
controversial observation of water vapor ions for a limited time on one day,
never to be repeated.

The three instruments were nominally identical, but did vary in energy and mass
levels. Mass resolution was coarse, but could identify water vapor, neon, argon.
The range went to 1000 AMU for Apollo 12, and to 120 AMU for Apollo 15.
Instrument descriptions and other results appear in the Preliminary Science
Report for each of the Apollo 12, 14, and 15 missions: NASA SP-235 (1970),
SP-272 (1971), and SP-289 (1972). Brief descriptions of the instruments and
archived data sets may be found via the NSSDCA Master Catalog for the
Apollo 12,
Apollo 14, or
Apollo 15 instruments.

J. W. Freeman of Rice University was the PI. NSSDCA's H. K. Hills was a member
of the experimenter team, and is supervising this effort. With an additional
processing step, these data will significantly extend the time coverage of the
presently archived SIDE data sets, and will include data not previously
examined. The level of effort spent on further processing will depend on the
interest shown in these data.

The previously-archived data sets each cover from 1.8 to 3.3 years, and
each is less than or about 300 MBytes. The newly-restored tapes cover
an additional 1 - 2.6 years for each data set, with the latest data
from November 1975.